NIPPON STEEL CORPORATION

This hot-rolled steel sheet has a predetermined chemical composition, in a microstructure at a position of ¼ from a surface in a sheet thickness direction, in terms of area %, martensite and tempered martensite is more than 92.0% and 100.0% or less in total, residual austenite is less than 3.0%, ferrite is less than 5.0%, an E value is 11.0 or more, an I value is less than 1.020, a CS value is −8.0×10 5 to 8.0×10 5 , a standard deviation of Mn concentrations is 0.60 mass % or less, at the surface, a number density of Si—Al—Cr oxides having a circle equivalent radius of 0.500 μm or more is 2.0×10 3 pieces/cm 2 or less, and a number density of Si—Al—Cr oxides having a circle equivalent radius of 0.005 μm to 0.050 μm is 1.0×10 5 pieces/cm 2 or more.

A frame member includes a closed cross-section part and a stress concentration part. The closed cross-section part includes a flat part and a ridge part. The flat part has a width of 70.0 mm or less. The stress concentration part is provided in at least one of the flat part and the ridge part. The Vickers hardness of a central portion in a sheet thickness direction of the flat part is 350 Hv or more. The standard deviation ratio is more than 1.0, and the standard deviation ratio is obtained by dividing the standard deviation of the frequency distribution of the Vickers hardness of a near-surface portion of the flat part by the standard deviation of the frequency distribution of the Vickers hardness of the central portion in the sheet thickness direction of the flat part.

This grain-oriented electrical steel sheet includes: a base steel sheet; and an insulating coating formed on a surface of the base steel sheet, in which the insulating coating includes an intermediate layer formed on a base steel sheet side and containing a crystalline metal phosphate, and a tension coating layer formed on a surface side of the insulating coating, the surface of the base steel sheet has an etch pit structure, an average thickness of the intermediate layer is 0.2 to 10.0 μm, an average thickness of the insulating coating is 2.0 to 10.0 μm, the tension coating layer contains a metal phosphate and silica, and an amount of the silica in the tension coating layer is 20 to 60 mass %.

A welded joint comprising a first steel sheet and a second steel sheet. A first plating layer is provided on a surface of the first steel sheet facing the second steel sheet, no plating layer is present on or a second plating layer is provided on a surface of the second steel sheet facing the first steel sheet, and a boundary plating layer is provided between the first steel sheet and the second steel sheet in a range of 0.5 mm from an end part of the corona bond toward an outside of the spot welded part. A higher tensile strength of a tensile strength of the first steel sheet and a tensile strength of the second steel sheet is 780 MPa or more, and an area ratio of a MgZn 2 phase at the cross-section of the boundary plating layer is 10% or more.

A steel sheet for hot stamping that further improves productivity of a hot-stamped member, has excellent appearance and has excellent spot weldability, and a hot-stamped member. The steel sheet for hot stamping includes, on the whole of at least one surface of the steel sheet, a surface-treated film whose emissivity at a wavelength of 8.0 μm at 25° C. is 60% or more, in which the surface-treated film contains carbon black, and one or more of oxides selected from a Zr oxide, a Zn oxide, and a Ti oxide, in which the carbon black and the oxides exist while being dispersed over the entire surface-treated film, the surface-treated film has a silica content of 0 to 0.3 g/m 2 , and when an adhesion amount of the carbon black and an adhesion amount of the oxides are set to X CB (g/m 2 ) and X Oxide (g/m 2 ), respectively, an equation (1) is satisfied.

An automobile panel 1 has a sheet-shaped outer panel 2 and a sheet-shaped inner panel 3 , and an interior member 30 arranged in a space S between the inner panel 3 and the outer panel 2 . The interior member 30 is an elongated member that extends in a first direction D 1 along the outer panel 2 , and includes a first end 41 that is one end in the first direction D 1 , and a second end 42 that is another end. The first end 41 has a first connecting portion 45 which is connected to the inner panel 3 . The interior member 30 has a second connecting portion 46 that is connected to the outer panel 2 , at a position that is separated from the first end 41 along the first direction D 1.

A bar steel according to an aspect of the present invention includes a matrix and a layer covering a surface of the matrix and containing Si, Cr, Fe, and O, in which the matrix contains, by unit mass %, C: 0.10 to 0.30%, Si: 0.51 to 2.40%, Mn: 0.50 to 1.50%, P: 0.050% or less, S: 0.050% or less, Cr: 0.05 to 2.00%, Al: 0.010 to 0.100%, N: 0.003 to 0.030%, and O: 0.0050% or less, the balance includes iron and impurities, and a Cr/Si mass concentration ratio of the layer is 0.10 or more.

A steel member has a predetermined chemical composition. In a case where a position corresponding to a depth of ¼ of a thickness from a surface in a thickness direction is defined as a ¼-depth position, a maximum B content in a range to a depth of 10 μm from the surface in the thickness direction is 5 times or more a B content at the ¼-depth position. In a case where a C content is measured from the surface in the thickness direction using GDS and the distance from the surface to a position where the C content is equal to a C content at the ¼-depth position for the first time is defined as a decarburization depth, the decarburization depth is 20 μm or more. The Vickers hardness at the ¼-depth position is in a range of 310 to 890.

This non-grain-oriented electrical steel sheet is a non-grain-oriented electrical steel sheet including a silicon steel sheet as a base material, wherein the silicon steel sheet has a predetermined mechanical property depending on a direction with respect to a rolling direction, and the difference between a maximum value and a minimum value of diameters of circular holes after punching with a substantially circular die is 0.20% or less of the average value of the maximum value and the minimum value.

A hearth roll for a continuous annealing furnace, the hearth roll comprising a thermal spray coating on a surface of the hearth roll, wherein the thermal spray coating comprises main components consisting of a Co-based alloy, a carbide of a transition metal, and a double oxide; and impurities, the double oxide consists of one or two types of a first double oxide consisting of Al and a rare earth element and a second double oxide consisting of a transition metal and a rare earth element, and when the main components are 100 mass %, a content of the Co-based alloy is 25 mass % or more and 50 mass % or less, a content of the carbide is 5 mass % or more and 30 mass % or less, and a content of the double oxide is 20 mass % or more and 45 mass % or less.